The present invention relates generally to printed circuit system boards and, more specifically, to method and apparatus for connecting a LVD SCSI device to a printed circuit system board.
A printed circuit system board (PCSB) is a printed circuit board used in a computer which contains the computer central processing unit (CPU) and is thus the primary circuit board of the computer. A printed circuit board is a device used for interconnecting separate circuitry, electrical components and devices used by a computer. A common standard used for computer input/output (I/O) communications is Low Voltage Differential (LVD) Small Computer Systems Interface (SCSI). (There are various types of SCSI buses other than LVD SCSI buses but it is to be understood that any reference to xe2x80x9cSCSIxe2x80x9d in this patent application, unless otherwise indicated, is a reference to LVD SCSI.) A typical LVD SCSI bus found on a PCSB includes a LVD SCSI controller device such as an ASIC which is mounted on one surface layer of the PCSB. The SCSI controller controls the LVD SCSI signals sent between the computer""s CPU and SCSI devices, such as hard drives, DVD drives, etc., which are connected to the SCSI bus. In currently used PCSB""s the LVD SCSI bus includes a number of signal traces or conductors which extend between the SCSI controller and a cable connector device mounted on the PCSB. The cable connector device is adapted to matingly receive a coupling member provided on one end of a computer cable. The other end of the computer cable is provided with another coupling member that is adapted to be attached to a cable connector mounted on a smaller, auxiliary, printed circuit board usually called a xe2x80x9cback plane.xe2x80x9d The auxiliary circuit board includes a series of signal traces which extend from the cable connector to one or more SCSI device connectors mounted on the back plane. The LVD SCSI device connector on the back plane may be a direct connector such as SCA-2 connector to which a LVD SCSI device may be directly mounted. The back plane further includes LVD SCSI terminator devices to which end portions of the SCSI traces are connected after connection thereof to the last direct connector. The terminators are active circuit devices which prevent signal reflection, etc.
Back plane mounted SCSI direct connectors provide a physically and electrically secure method for operably connecting a SCSI device to a computer. The fact that the back plane is on a separate board from the PCSB adds flexibility to the computers design since the back plane is small and may be moved where ever the associated SCSI device is to be located. However back planes add cost to a computer system because they must be separately fabricated. Also, because they contain SCSI terminators, they are considered active PCB""s which must be tested separately from the PCSB, adding to the overall cost. The cable between the PCSB and the cable connectors provided on the PCSB and the back plane also add to overall cost.
Another problem discovered by applicants with regard to the use of back plane mounted SCSI direct connectors is that such assemblies may frustrate certain SCSI bus noise management strategies discovered by applicants. Applicants have discovered that by isolating certain SCSI bus signals from other SCSI bus signals on the PCSB that a significant improvement in SCSI device performance may be achieved. However when these signals are conventionally routed through SCSI computer cabling to a back plane the improved performance is typically lost because the critical signal isolation is lost in the cabling.
The above discussed problems with SCSI device mounting and operation, which applicants were the first to fully appreciate, may be overcome by mounting SCSI direct connectors and associated terminators directly on the computer""s PCSB rather than a separate back plane. Such an assembly obviates the need for SCSI connector cables as well as the back plane. Also, when such a PCSB assembly is used, applicants have discovered that SCSI bus performance may be considerably improved because of the elimination of certain noise associated with SCSI cable connections. Furthermore, when careful trace isolation of the RESET, SELECT and BUSY signals of the SCSI bus is maintained, even better bus performance may be achieved. This latter achievement is generally not achievable when cable connection is used because the circuit designer has no control over signal routing in the computer cables which are built to a preset industry standard.
Thus the invention may comprise a PCSB assembly including a PCSB; a plurality of LVD SCSI bus signal traces formed in the PCSB; and a LVD SCSI direct connector mounted on the PCSB and electrically connected to the plurality of traces.
The invention may also comprise a method of making a PCSB assembly including: forming a plurality of LVD SCSI bus signal traces on a PCSB; mounting a LVD SCSI direct connector on the PCSB; and electrically connecting the plurality of traces to the LVD SCSI direct connector.
The invention may also comprise a PCSB assembly including a PCSB; means for conducting LVD SCSI bus signals formed in the PCSB; and means for directly mounting a LVD SCSI device on the PCSB electrically connected with the means for conducting LVD SCSI bus signals.
The invention may also comprise a computer including a printed circuit board; a computer central processing unit operably mounted on the printed circuit board; a LVD SCSI bus controller mounted on the printed circuit board; a LVD SCSI direct connector mounted on the printed circuit board; a plurality of LVD SCSI signal traces electrically connected to the LVD SCSI bus controller and to the LVD SCSI direct connector; and a LVD SCSI device directly operably mounted in the LVD SCSI direct connector.